Considerable research and development has been applied to delivery of drugs to economically-important animals. Drugs have been formulated in numerous ways for administration, both transdermally and by ingestion. Current reviews are provided by Banaker (Banaker, U. V. [1987] Amer. Pharm. 27:39-42) and by Breimer (Breimer, D. D. [1986] Proc. 3rd Congress European Assoc. for Vet. Pharm. and Toxicol. 75-84). For administration by ingestion, drugs have been incorporated into liposomes (Freeman, F. J., Hayward, J. A. and Chapman, D. [1987] Biochem. Biophys. Acta. 924:341-351), into granules prepared by fluidized bed coating with materials such as ethyl cellulose (Friedman, M., Donbrow, M. and Samuelon, Y. [1979] J. Pharm. Pharmacol. 31: 396-399), and into various types of microcapsules (Arnold, R. G. [1984] Appl. Biochem. Biotechnol. 10: 237-243).
A consequence of the development of this technology is the considerable expense incurred in processing drugs into an appropriate form for delivery. Polypeptide (protein) drugs are unusually difficult to deliver because they are relatively labile and can be degraded by the host before they can be delivered to their site of action, such as intestines, stomachs, etc.
There is a continuous need for economical and efficient drug delivery systems for both animals and humans.